The present invention relates to a solid oxide fuel cell and particularly to a fuel cell having preferential cooling of the seals to maintain low cell temperature difference across the seal and cell and interconnects formed of different materials in the cathode flow field to control heat transfer and to yield uniform cell temperature.
A fuel cell is an electrochemical device in which a hydrogen or a hydrocarbon fuel is electrochemically reacted with air or oxygen to produce electricity, heat and water. A fuel cell typically includes a cathode flow field for flowing oxidant, an anode flow field for flowing hydrogen or a hydrocarbon fuel and a cell between the cathode and anode flow fields typically formed of a hard ceramic electrolyte. Oxygen ions are formed at the oxidant electrode i.e., the cathode, and when the hydrogen or other hydrocarbon fuel is passed over the fuel electrode, i.e., the anode, the oxygen ions migrate through the hard ceramic electrolyte to oxidize the fuel, transforming the hydrogen to water and carbon monoxide to carbon dioxide while releasing electrons. The electrons move out through an external circuit to create electricity. High seal temperature and high temperature gradients across the seal however can lead to fuel leakage, anode oxidation and performance degradation. Cooling the seals to maintain lower uniform temperature can eliminate those issues. Further, high temperature gradients across the cell can lead to high thermal stress which, in turn, can result in cell cracking and reduced stack life. Improved heat transfer communication between the cell and the interconnects i.e. the ribs of the cathode flow field defining the oxidant flow passage, can reduce the thermal gradient and prevent cell cracking. Accordingly, there is a need for improving the seal and managing the thermal gradients across the cell.